Control of pipe tension between extruder die and take-up coiler

ABSTRACT

A process and apparatus for minimizing breakage and stretching during the high speed production of plastic pipe is provided wherein a pipe is extruded at a first linear rate of speed, a slack segment is established and maintained between the extruder and a pipe winder, and the pipe is taken up on the winder at a second linear rate of speed which is the same as or different from the first rate, wherein the pipe is taken up on the winder responsive to the degree of slack in the slack segment.

This invention relates to the extrusion of plastic pipe. In one aspect,this invention relates to an apparatus for minimizing breakage andstretching of plastic pipe during its production. In another aspect,this invention relates to an apparatus for extruding a plastic pipe andfor winding the pipe onto a winding roll while controlling tension onthe pipe.

Recent advances in extrusion technology have made it possible to extrudesmall diameter plastic pipe at relatively high rates. For example, it isnow possible to extrude pipe having a diameter between 1/2" and 11/8" ata rate of up to approximately 180 inches per minute. This high extrusionrate has, however, created problems of breakage and stretching of thepipe, due in large part to failure of the pipe take-up coiler to respondto changes in the extrusion rate. It is, therefore, desirable to be ableto extrude a small diameter plastic pipe and wind same onto a take-uproll wherein isolation is provided between the extruder and the take-uproll, whereby breakage and stretching are minimized, if not completelyeliminated.

It is another object of the present invention to provide an improvedapparatus for extruding small diameter plastic pipe and for winding sameonto a take-up roll.

It is a further object of this invention to provide an apparatus forisolating the tension in an extruded plastic pipe between the extruderand a take-up roll.

Other objects, aspects and advantages of the present invention will bereadily apparent to those skilled in the art from the reading of thefollowing disclosure, appended claims and attached drawings.

It has now been found that breakage and stretching of plastic pipe canbe minimized, if not eliminated, by isolating the pipe extruder meansfrom the winding means. Thus, tension in the pipe created by the windingmeans is not transmitted through the pipe to the extruder means.

Isolation between the extruder means and the winding means is providedby a slack segment. The degree of slack in the slack segment is measuredby sensing means and the take-up speed of the winding means is variedresponsive thereto.

More particularly, the present invention provides an improved apparatusfor use in a process for minimizing breakage and stretching of plasticpipe during the production of same which comprises:

(A) EXTRUDING A PLASTIC PIPE FROM AN EXTRUDER MEANS AT A FIRST LINEARRATE OF SPEED;

(B) ESTABLISHING AND MAINTAINING A SLACK SEGMENT IN THE PIPE BETWEEN THEEXTRUDER MEANS AND A WINDING MEANS, THEREBY ISOLATING THE WINDING MEANSFROM THE EXTRUDED MEANS; AND

(C) TAKING UP THE PIPE ONTO A WINDING MEANS AT A SECOND LINEAR RATE OFSPEED WHICH IS THE SAME AS OR DIFFERENT FROM THE FIRST RATE, WHEREIN THEPIPE IS TAKEN UP ONTO THE WINDING MEANS RESPONSIVE TO THE DEGREE OFSLACK IN THE SLACK SEGMENT.

In one embodiment of this invention, the slack segment is established byallowing the pipe to arc between the extruder means and the windingmeans. The length of the arc, measured along the plastic pipe, shouldgenerally be at least about 1.02 times the straight line distancebetween the two points of suspension, i.e., the extruder means and thewinding means. The maximum length of the arc is, of course, determinedby the height of the suspension points above the floor under the lowestpoint of the arc.

In another embodiment of this invention, the slack segment isestablished by forming the pipe into a closed loop between the extrudermeans and the winding means. The close loop can be any convenient size,so long as the pipe is not kinked in its minimum loop configuration. Ingeneral the loop should have a minimum inside diameter of at least about40 inches, preferably at least about 48 inches. The maximum size of theclosed loop is determined by the means for maintaining the pipe in aclosed loop. In general, the maximum inside diameter is about 10 feet,or greater, depending upon the physical size of the loop maintainingmeans.

The apparatus of the present invention will be better understood byreference to the accompanying drawings, of which FIG. 1 is a side viewof an apparatus for extruding and winding a plastic pipe wherein thepipe winder is isolated from the extruder by a slack segment of pipe.FIG. 2 is a side view of an apparatus for extruding and winding aplastic pipe, wherein isolation between the extruder and the pipe winderis provided by a closed loop. FIG. 3 is a side view of the loop sizesensing means employed in the apparatus of FIG. 2. FIGS. 4 and 5 are topand end views of the apparatus illustrated in FIG. 3, taken at 4--4 and5--5, respectively, of FIG. 3.

Referring now to FIG. 1, a plastic pipe 2 is shown as it emerges fromextruder die 4. A slack segment is formed in the pipe 2, as at 6, andthe pipe is taken up by winding means 8.

The winding means 8 has a frame means 10 for mounting and a motor means12 adapted to effect rotation of winding roll 14 whereby the pipe iswound onto winding roll 14.

The motor means 12 can be electric, hydraulic or pneumatic. The speed ofmotor means 12 is controlled by appropriate electrical control means,hydraulic control means or pneumatic control means, respectively, ashereinafter discussed.

The pipe 2 can be extruded by any suitable extruder, such as a screw-,ram-, or dynamic-type extruder such as, for example, the type disclosedin U.S. Pat. No. 3,387,073, which is incorporated herein by reference.

It is important that the slack segment 6 be present in a controlledmagnitude; therefore, the upper and lower limits of segment 6 aremonitored by any suitable means, such as, for example, photo-responsivecells, 16 and 18, respectively, or the like. In FIG. 1, the upper limitof the slack segment 6 is sensed by photo-responsive cell 16 positionedopposite light source 20, while the lower limit of the segment iscontrolled by photo-responsive cell 18, positioned opposite light source22. It is understood, of course, that the photo-responsive cells andsources are positioned so as to detect the upper and lower limits of theslack segment.

The output of the cells 16 and 18 are coupled to the power source 24 formotor means 12. In this fashion if slack segment 6 becomes too large,motor means 12 is caused to run faster to take up the unwanted portionof slack. Conversely, if the slack segment becomes too small, motormeans 12 is caused to run slower to allow the slack segment to becomelarger.

In one embodiment of this invention, the pipe 2 is passed through aconstant tensioning means 26 positioned just ahead of the winding means8 in order to maintain the pipe under appropriate tension for propercoiling on the winding roll 14. The constant tensioning means 26 can bea drag-pinch-roller arrangement comprising an idler roller 28 and abraked roller 30 having in association therewith an adjustable brakingmeans 32. The rollers 28 and 30 have profiles to fit the outer contourof the pipe 2. The desired winding tension on the pipe is achieved byvarying the braking force applied to the wheel 30 by braking means 32.

In another embodiment of this invention, a pipe pulling means 34 isemployed after the die 4 and ahead of the slack segment 6 to increasethe extrusion rate by pulling the pipe 2 with a constant force from thedie. The pulling means 34 comprises an idler roller 36 and a drivenroller 38 which is driven at a preset speed by a motor means 40.

FIG. 2 illustrates an alternative embodiment of this invention whereinisolation between the die 4 and the take-up roll means 8 is provided bya closed loop 42. In this embodiment, the loop sensing means 44, thepipe pulling means 34 and the constant tensioning means 26 are mountedon a base 46. The loop sensing means 44 is shown in greater detail inFIGS. 3-5.

As shown in FIGS. 3, 4 and 5, the loop sensing means 44 is adjustablysupported on the base 46 by vertical support means 48 and 50. The loopsensing means comprises a mounting base assembly 52 adjustably mountedto the vertical support means 48 and 50, and a pivotally mounted sensingarm 54. Arm 54 is fastened or secured to shaft 56, shaft 56 being, inturn, journaled for arcuate rotation by means of bearings 58 and 60which are attached to base assembly 52.

One end of the sensing arm 54 has a contacting roller 62 for contactingthe pipe loop. The contacting roller 62 can be journaled for rotation bysuitable bearings, not shown. The opposite end of the sensing arm 54 hasa counterweight 64 of sufficient weight to generally impart an overallcounterclockwise movement to the sensing arm 54. A drive sprocket 66 issecured to shaft 56 between the sensing arm 54 and bearing 58.

Signals generated by movement of the sensing arm 54 are transmitted tomotor controlling means 68 through drive sprocket 66, drive chain 70,driven sprocket 72, and speed reducing means 74, the driven sprocket 72being attached to the input shaft 76 of speed reducing means 74 andmotor controlling means 68 being attached to the output shaft 78 ofspeed reducing means 74.

Motor means 12 can be electric, hydraulic or pneumatic, and motorcontrolling means 68 can be a rheostat or potentiometer, hydraulic valveor pneumatic valve, respectively. By coupling the sensing arm 54 throughthe sprockets 66 and 72, drive chain 70 and speed reducing means 74 tothe motor controling means 68, in the manner illustrated, minorfluctuations in the size of the loop segment 42 are minimized, thusreducing fluctuation in the speed of motor means 12.

Referring again to FIG. 2, power, either electrical, hydraulic, orpneumatic, is supplied to motor control means 68, from a source notshown. Controlled power is then transmitted to motor means 12 via line76. Thus, if the slack loop 42 becomes too large, the contacting rollerend of sensing arm 54 moves upwardly. This upward motion is translatedto rotary motion and transmitted to motor control means 68 through drivesprocket 66, drive chain 70, driven sprocket 72 and speed reducing means74. The motor controlling means then acts to increase the speed of motormeans 12, either by increasing voltage, hydraulic flow or pneumaticflow, depending upon the type motor and motor controller used.Conversely, if the slack loop becomes too small, the contacting rollerend of sensing arm 54 moves downwardly, thereby causing motor drivemeans 12 to run slower to allow the slack loop 42 to become larger.

The apparatus of this invention is particularly suitable for the highspeed extrusion and take-up of small diameter, flexible thermoplasticpipe, such as polyethylene pipe. By small diameter pipe it is meant pipehaving an outer diameter of up to about 3 inches. By high speed, it ismeant an extrusion rate of up to about 200 inches per minute or greater,generally from 50 to 180 inches per minute. For example, a 1-inch pipecan be extruded at speeds up to about 200 inches per minute and 3-inchpipe can be extruded at a rate of about 50 inches per minute.

Reasonable variations and modifications, which will be apparent to thoseskilled in the art, can be made in this invention without departing fromthe spirit and scope thereof.

I claim:
 1. Apparatus for extruding an elongated plastic pipe and forwinding said pipe onto a winding roll comprising, in combination,(a)pipe extrusion means; (b) winding means comprising said winding roll,frame means for mounting said winding roll and motor means for rotatingsaid winding roll to wind said pipe onto said winding roll; (c) meansfor establishing and maintaining a slack segment in said pipe betweensaid extrusion means and said winding means; (d) sensing means forsensing the degree of slack in said slack segment; and (e) control meansfor actuating said motor means responsive to said sensing means.
 2. Theapparatus of claim 1 additionally comprising means for applying tensionto said pipe between said slack segment and said winding roll.
 3. Theapparatus of claim 1 additionally comprising means for applying apulling force to said pipe between said extruder means and said slacksegment.
 4. The apparatus of claim 1 wherein said slack segment has anarc shape and wherein said sensing means comprise at least twophoto-responsive cells, one of said cells being disposed above saidslack segment and one of said cells being disposed below said slacksegment.
 5. The apparatus of claim 1 wherein said slack segment is aclosed loop and wherein said sensing means is adapted to determine theimmediate inner diameter of said loop, said sensing means comprising(a)a supporting structure; (b) a bracket assembly adjustably mounted uponsaid support structure and having means for securing said bracketassembly to said support structure; (c) sensing arm means mounted forpivotal arcuate rotation on said bracket assembly and having a first endthereof adapted for contact with said pipe to determine the immediateinner diameter of said loop; (d) means for maintaining said first end ofsaid arm means in running contact with said pipe; (e) means forgenerating a signal responsive to the position of said arm means and forproviding said signal to said control means; (f) means for connectingsaid sensing arm means to said signal generating means; and (g) loopguide means mounted upon said supporting structure for maintaining saidloop.
 6. The apparatus of claim 5 additionally comprising means forapplying tension to said pipe between said loop and said winding roll.7. The apparatus of claim 5 additionally comprising means for applying apulling force to said pipe between said extruder means and said loop. 8.An apparatus for maintaining a loop segment in a flexible pipe and fordetermining the size of said loop segment comprising:(a) a supportingstructure; (b) a bracket assembly adjustably mounted upon said structureand having means for securing said bracket assembly to said structure;(c) sensing arm means mounted for pivotal arcuate rotation on saidbracket assembly and having a first end thereof adapted for contact withsaid pipe to determine the immediate inner diameter of said loop; (d)means for maintaining said first end of said arm means in contact withsaid pipe; (e) means for generating a signal responsive to the positionof said arm means; (f) means connecting said sensing arm means to saidsignal generating means; and (g) loop guide means for maintaining saidloop mounted upon said supporting structure.
 9. The apparatus of claim 8wherein said supporting structure comprises at least two verticalsupport members, said members spaced apart at least a minimum distancewhereby said loop passes between said members without resistance. 10.The apparatus of claim 9 wherein said means for maintaining said firstend of said arm means in contact with said pipe is a counterbalance onthe second end of said arm.